/// <reference types="node" />
/**
 * Determine if a value is an Array
 *
 * @param {Object} val The value to test
 * @returns {boolean} True if value is an Array, otherwise false
 */
export declare function isArray<T>(val: unknown): val is T[];
/**
 * Determine if a value is an Object
 *
 * @param {Object} val The value to test
 * @returns {boolean} True if value is an Object, otherwise false
 */
export declare function isObject(val: unknown): val is object;
export declare const isDate: (thing: unknown) => thing is Date;
/**
 * Determine if a value is a Function
 *
 * @param {Object} val The value to test
 * @returns {boolean} True if value is a Function, otherwise false
 */
export declare function isFunction(val: unknown): val is Function;
/**
 * Determine if a value is a Stream
 *
 * @param {Object} val The value to test
 * @returns {boolean} True if value is a Stream, otherwise false
 */
export declare function isStream(val: unknown): boolean;
declare interface Headers {
    [key: string]: string | number | boolean;
}
declare class FormData {
    getHeaders(userHeaders?: Headers): Headers;
}
/**
 * Determine if a value is a FormData
 *
 * @param {Object} thing The value to test
 * @returns {boolean} True if value is an FormData, otherwise false
 */
export declare function isFormData(thing: unknown): thing is FormData;
/**
 * Determine if a value is a URLSearchParams object
 * @function
 * @param {Object} val The value to test
 * @returns {boolean} True if value is a URLSearchParams object, otherwise false
 */
export declare const isURLSearchParams: (thing: unknown) => thing is URLSearchParams;
/**
 * Iterate over an Array or an Object invoking a function for each item.
 *
 * If `obj` is an Array callback will be called passing
 * the value, index, and complete array for each item.
 *
 * If 'obj' is an Object callback will be called passing
 * the value, key, and complete object for each property.
 *
 * @param {Object|Array} obj The object to iterate
 * @param {Function} fn The callback to invoke for each item
 */
export declare function forEach<T extends object>(obj: T | undefined, fn: (val: T[keyof T], key: keyof T, obj: T) => void): void;
export declare function forEach<T extends S[], S>(obj: T | undefined, fn: (val: S, key: number, obj: T) => void): void;
/**
 * Remove byte order marker. This catches EF BB BF (the UTF-8 BOM)
 *
 * @param {string} content with BOM
 * @return {string} content value without BOM
 */
export declare function stripBOM(content: string): string;
/**
 * Resolve object with deep prototype chain to a flat object
 * @param {Object} sourceObj source object
 * @param {Object} [destObj]
 * @param {Function} [filter]
 * @returns {Object}
 */
export declare function toFlatObject(sourceObj: unknown, destObj: unknown, filter: (sourceObj: unknown, destObj: unknown) => boolean): unknown;
export {};